Initial Crystallization Temperature Research Articles

Influence of Initial Crystallization Temperature of Form II on the Nucleation and Growth of Form I IPBu Crystals during II–I Phase Transition

Influence of Initial Crystallization Temperature of Form II on the Nucleation and Growth of Form I IPBu Crystals during II–I Phase Transition

In Situ Compatibilization of Isotactic Polypropylene and High-Density Polyethylene by a Melt Cobranching Reaction

Incompatible polypropylene (PP) and polyethylene (PE) are difficult to separate in mixed recycling streams such as waste plastic packaging, which makes polyolefin mixtures unsuitable for high-quality products. In this work, based on the free radical branching reaction, a co-branching reaction of isotactic polypropylene (iPP) and high-density polyethylene (HDPE) blends was carried out in the presence of the peroxide, free radical regulator and multifunctional acrylate monomer, and a star-like long-chain branching (LCB) copolymer was obtained. The effect of in situ compatibilization on the structures and mechanical properties of iPP/HDPE was investigated, and the compatibilization mechanism was discussed. Results showed that the mechanical properties of the modified blends were largely improved, and efficient in-situ compatibilization of iPP and HDPE could be taken place in a wide process window. Moreover, the sizes of the dispersed phase in the modified blends were clearly decreased, and the interfacial thickness increased. Compared with the pure iPP/HDPE blend, the initial crystallization temperature of iPP in the modified iPP/HDPE blend was increased, and long branched chains of the LCB copolymers were physically entangled with the chemical identical homopolymers or even participated in the crystallization of iPP and HDPE. Thanks to the in situ compatibilization strategy, the compatibility of iPP/HDPE was significantly improved.

Influence of water vapor on continuous cooling crystallization characteristics of coal ash slag

The influence of water vapor on crystallization characteristics and kinetics of two synthetic ashes during continuous cooling were investigated by the single hot thermocouple technique (SHTT) and differential scanning calorimetry (DSC) under Ar with 0%, 10%, 20% and 30% H2O. Anorthite (CaAl2Si2O8) and gehlenite (Ca2Al2SiO7) were the major crystalline phases for the slag with 75.44% (YL) and 29.72% (YZ) silicon-aluminum levels, respectively. As the water vapor content increased, the initial crystallization temperature (Ton) and the maximum crystal ratio (Xmax) of the YL slag increased, while it decreased for the YZ slag. The continuous cooling crystallization kinetics was determined based on DSC data. The effect of water vapor proportion on crystallization temperature of the slag showed a similar trend with that on the TCV. As the water vapor proportion increased, the obtained values of crystallization activation energy (Ec) of the YL slag decreased, while it increased for the YZ slag. The influence of water vapor on crystallization kinetics of coal ash slag showed its dependence on nucleation and crystal growth style during continuous cooling. The results well explained the influence of water vapor on crystallization behavior of anorthite and gehlenite crystalline phases as well as its effects on slag viscosity and TCV in our previous studies.

Comparative study on high temperature thermal stability of quaternary nitrate-nitrite mixed salt and Solar salt

Molten salts are applied in solar thermal power plant as heat transfer and heat storage medium. In this work, the thermal stability of quaternary nitrate-nitrite (QNN) mixed salt and Solar salt are studied under three constant temperature conditions (500 °C, 565 °C, 600 °C) for 1008h. The results show that the mass ratio of N O 2 − 1 / N O 3 − 1 plays an important role in the thermal physical properties of nitrite/nitrate molten salt. The mass ratio of N O 2 − 1 / N O 3 − 1 in Solar salt increases with the increasing of working temperature, which results in the decreasing of melting point and initial crystal temperature and the increasing of decomposition temperature. The average values of melting point and initial crystal temperature of QNN mixed salt are maximum 119 °C and 24 °C lower than that of Solar salt. Meanwhile, the maximum increase of average values of specific heat and thermal conductivity of QNN mixed salt are 14.26%, 8.18% compared with its base salt, respectively. When the working temperature is higher than decomposition temperature, average values of specific heat and thermal conductivity of Solar salt decrease because of the acceleration of nitrite formation. The viscosity values of QNN mixed salt and Solar salt decrease with the increasing of temperature. Based on the comparative analysis, QNN mixed salt has good application value in practical engineering applications. • The long-time thermal stability of QNN mixed salt and Solar salt are studied. • Nitrite/nitrate ratio plays an vital role in molten salt thermal physical property. • The thermal physical performance of QNN mixed salt is better than Solar salt.

Investigation on thermal performance of quaternary nitrate-nitrite mixed salt and solar salt under thermal shock condition

Molten salts are subjected to heating-cooling thermal shock cycle in the operation of concentrating solar power (CSP) plant. In this work, the quaternary nitrate-nitrite (QNN) mixed salt and Solar salt are comparatively studied under different thermal shock conditions. After 500 thermal shock test cycles, morphological and structural analysis of samples are carried out by wavelength dispersive x-ray fluorescence (WD-XRF), Fourier-transform infrared (FTIR), x-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Meanwhile, thermos-physical properties of samples are comparatively analyzed. The results show the average melting point and average initial crystal temperature of QNN mixed salt are maximum 135 °C, 82.6 °C lower than that of Solar salt, respectively. The decomposition temperature of QNN mixed salt is maximum 52.1 °C higher than that of Solar salt. The specific heat of QNN mixed salt increases with the increasing of thermal shock temperature. The specific heat and thermal conductivity of QNN mixed salt maximally increase 15.46% and 9.8% compared with its base salt, respectively. Meanwhile, the thermal conductivity and viscosity of QNN mixed salt are slight higher than that of Solar salt. The Solar salt viscosity decreases with the increasing of thermal shock temperature.

Comparison of hot pressing sintering and conventional powder-sintering in preparation of CaO-Al2O3-SiO2-Fe3O4-R2O glass ceramics

The influences of different alkali metal oxides, sintering methods, process conditions on the crystallization behavior and densification of CaO-Al2O3-SiO2-Fe3O4-R2O (R=Na, K) glass ceramics were investigated. It can be concluded that the initial crystallization temperature and crystallization peak temperature of glass containing K2O were higher than those of glass containing Na2O, respectively. The increase of sintering temperature promoted the precipitation of crystalline phase in glass ceramics, meanwhile, the crystalline phases transformed from single magnetite to magnetite and CaFeSi2O6. The glass ceramics obtained by powder-sintering showed a low degree of densification. The fully dense glass ceramics containing Na2O can be obtained by hot pressing sintering above 680 °C for 2 h. However, due to the high viscosity of the glass containing K2O, the degree of densification of K2O containing glass ceramics was relatively low even after the hot pressing sintering. Magnetite based glass ceramics can be used as candidates for magnetic materials.

Study on the crystallization mechanism of TiNiNb amorphous alloy

In order to study the crystallization mechanism of Ti44Ni47Nb9 amorphous alloy. Firstly, the Ti44Ni47Nb9 amorphous alloy was prepared by mechanical alloying (High energy ball milling). Then, the effect of amorphous mechanism and annealing process on the alloy was analyzed. The results showed that the crystallization effect of amorphous powder was the best, when the annealing process was 575 °C and the temperature was kept for 30 min. The glass transition temperature Tg, the initial crystallization temperature Tx and the peak crystallization temperature Tp all increased with the increase of the heating rate, showing obvious kinetic effects. The apparent activation energies of the glass transition, initial crystallization and crystallization peak were respectively 150.76, 146.57 and 331.74 kJ/mol by using the Ozawa equation.

Analysis on the corrosion characteristic and risk in atmospheric tower using Aspen plus software

The corrosion problem of atmospheric tower, as the main distillation unit in refineries, has attracted much researchers’ attention. Based on the Braun K-10 thermodynamic model and Peng-Robinson equation, the process simulation was performed to predict the corrosion risk in the atmospheric tower. The distributions of the temperature, phase state and corrosive components in the multi-component stream were analyzed. The results have shown that the temperature distribution in the atmospheric tower is linearly correlated with the processing capacity and the properties of raw materials. The feed with corrosive medium can reduce the tower temperature by 15 °C on average. In addition, it has been found that both of the ammonium salt under-deposited corrosion and dew point corrosion exist in the atmospheric tower. The initial crystallization temperature of ammonium salt is located at the 15th stage of tray, and the dew point corrosion region is among the 1st and 15th stage of tray. The prediction results of the high-risk corrosion areas are coincided to the actual corrosion regions.

Effect of Water on Crystallization and Melting of Telechelic Oligo(ε‐caprolactone)s in Ultrathin Films

AbstractThe thermal behavior of ultrathin, semi‐crystalline films of oligo(ε‐caprolactone)s (OCLs) with hydroxy or methacrylate end groups, is studied by the Langmuir technique in dependence on mean molecular areas and crystallization temperatures. The films on solid substrate as obtained by Langmuir–Schaefer transfer exhibit different lamellar thicknesses, crystal number densities, and lateral sizes. The melting temperature of OCL single crystals at the water and solid surface is proportional to the inverse crystal thickness and generally lower than in bulk PCL. An influence of OCL end groups on the melting behavior is observed mainly at the air–solid interface, where methacrylate end capped OCL melts at lower temperatures than hydroxy end capped OCL. Comparing the underlying substrate, melting/recrystallization of OCL ultrathin films is achievable at lower temperatures at the air–water interface than at the air–solid interface, where recrystallization is not identifiable. Recrystallization at the air–water interface generally occurs at higher temperature than the initial crystallization temperature. The surface pressure, as an additional thermodynamic variable, seems to further affect the crystallization behavior, with crystal thickness and lateral growth rate increasing with surface pressure. The results presented here are important when designing temperature‐sensitive or active nanostructured materials or interfaces based on OCL.

Effect of rare earth oxide on the crystallization behavior of CaO-Al2O3-based mold flux for rare earth heat-resistant steel continuous casting

New CaO-Al2O3-based mold flux for rare earth steel continuous casting was devised to restrain the slag-steel interface reaction. The effect of Ce2O3 on the crystallization behavior were investigated. The continuous cooling transformation tests show that the addition of Ce2O3 not only reduces the critical cooling rate of the mold flux but also reduces the initial crystallization temperature. Besides, the distribution of the initial crystallization temperature became more stable. The temperature time transformation tests show that the crystallization incubation time is slightly increased, the addition of Ce2O3 inhibit the isothermal crystallization process to a certain extent. The crystalline phases changed from LiAlO2+CaO to LiAlO2+CaCeAlO4. The precipitation of CaO was restrained by adding Ce2O3. With the combination of Ca2+, Ce3+, and [AlO69−]-octahedron units, CaCeAlO4 formed and precipitated in the crystallization process. Besides inhibiting the crystallization of CaO-Al2O3-based mold flux, adding rare earth oxide also can reduce the viscosity and the breaking temperature.

Transition temperature and thermal conduction behavior of slag in gasification process

The thermal conduction behavior of slags affects the stable operation of entrained-flow gasifier. The thermal conduction behavior of five-element synthetic slag system with four series variable composition was systematically studied. The turning point of thermal conductivity changing with temperature is observed in each sample, where thermal conductivity is at peak value. The temperature of this point is defined as the transition temperature Tct, which is determined by the intersection point of two fitting lines based on two mechanisms. When T > Tct, the thermal conductivity is exponentially related to the reciprocal of temperature. With decrease of temperature, two different downward trends of thermal conductivity are observed, which is probably caused by the difference of crystal precipitating rate, and the effects of glassy and crystal state also cannot be neglected. When T < Tct, the thermal conductivity is positively linear with temperature. It was found that Tct is between the initial crystallization temperature and the ash melting point, where thermal conductivity of slag begins to be affected by the crystal thermal conduction. A prediction model of the transition temperature is established based on the liquid phase temperature without the requirement of experimental tests and verified by five actual coal ashes.

In-situ Deposition of Novel Amorphous Al &lt;sub&gt;2&lt;/sub&gt;O &lt;sub&gt;3&lt;/sub&gt;-Gap Ceramic Coating With Excellent Microstructure Stability and Uniformity via Atmospheric Plasma Spraying

A novel Al2O3-GdAlO3(GAP) amorphous ceramic coating was in-situ prepared via atmospheric plasma spraying. The Al2O3/Gd2O3 sprayable powders possessed excellent sphericity and fluidity after heat treatment at 900 °C for 2 h with no solid-phase reaction, which indicated the Al2O3-GAP coating deposition process was greatly simplified. The Al2O3-GAP amorphous coating showed high glass transition temperature (1155.1 K), initial crystallization temperature (1179.2 K), local activation energy (847.6 kJ/mol) and nucleation resistance (88.3). Compared with almost all amorphous materials, the Al2O3-GAP amorphous coating possessed greater crystallization activation energy, which was conducive to its high temperature microstructure stability. Furthermore, the hardness and elastic modulus of Al2O3-GAP coating fluctuated with a tiny range as increasing the nanoindentation depth from 500 nm to 2000 nm with ten different nanoindentation experiments, which denoted excellent microstructure and mechanical performance uniformity of the coating. Therefore, the results showed that the Al2O3-GAP amorphous coating had better potentials for large-scale engineering application under harsh service conditions.Keywords: Plasma spraying; Amorphous oxides; Al2O3-GAP coating; High temperature microstructure stability; Performance uniformity

Mixing effect of slag compositions and additives on crystallization of mold fluxes for Ti-bearing steels

Increasing titanium content enhances the high temperature corrosion resistance and strength of steel and alloy, whereas it is prone to induce the severe slag/metal reaction during continuous casting, causing great property change of mold flux. With the aim of understanding their influence rule to further control perovskite precipitation for industrial application, in this paper, the mixing effect of TiO2, basicity and additives including BaO, B2O3 and Li2O on the crystallization characteristic of mold flux has been investigated through combined analysis of DSC, XRD and SEM-EDS. The results indicated that increase of TiO2 from 0 consecutively decreased crystallization temperature and crystal size of cuspidine but accelerated initial precipitation and crystallization temperature and size of perovskite since 8% TiO2. Increase of basicity in the case of 12% TiO2 enhanced the overall crystallization capacity regarding crystallization temperature and size of cuspidine and perovskite. Under moderate basicity and high TiO2 content, B2O3 has strongest suppression effect on mold flux crystallization, BaO has decreasing suppression effect and Li2O has weakest suppression effect compared with them. For different TiO2 pickup and basicity of mold flux, varying strategies were suggested to adjust the crystallization considering the mixing effect of mold flux compositions and additives.

Microscopic hardness and dynamic mechanical analysis of rapidly solidified Fe-based amorphous alloys

A systematic work was conducted to investigate the nanoindentation, dynamic relaxation, high-temperature rheological behavior, and structural relaxation after high-temperature deformation of Fe52-xCo20NixB19Si5Nb4 (x = 7,12,17, labeled as S1, S2 and S3) metallic glass. The results of nanoindentation indicate that the hardness of amorphous alloy reduces first and then enhances with the increase of Ni content. S1 alloy exhibits the highest hardness of 13–16 GPa, while relatively excellent compression plasticity is reached in S2 alloy. Besides, the glass transition temperature (Tg), initial crystallization temperature (Tx), α relaxation temperature (Tα) and internal friction change at different temperatures were determined and compared. The critical temperature, strain rate during non-Newton to Newtonian rheology and Newtonian viscosity at Tg temperature were discussed. Moreover, it was found that the activation volume improved and then decreased due to structural relaxation. At last, combined with the width of the supercooled liquid region, relaxation behavior and rheological viscosity at high temperature, the microstructure evolution of the three kinds of metallic glass under Tg temperature deformation was explained.

Thermodynamics and kinetics of REEs in CaO–SiO2–CaF2–Ce2O3 system: A theoretical basis toward sustainable utilization of REEs in REE-Bearing slag

Sustainable utilization of rare earth elements (REEs) in REE-bearing slag has recently attracted significant interest in industries and research community. However, few thermodynamic and kinetic data have been reported for REEs systems, which greatly limits the sustainable utilization of REE-bearing slag in ceramics and other fields. Therefore, the isothermal phase diagram of CaO–SiO2–CaF2–Ce2O3 system was constructed, and the phase equlibria data of REEs in REE-bearing slag were provided in this study. On this basis, the phase equilibria of the RE-phase in CaO–SiO2–CaF2–Ce2O3 system was investigated, the exact initial crystallization temperature of cefluosil (Ce9.33-xCax(SiO4)4O5-0.5xF2) in the system was 1450 K and the cefluosil crystals were in a hollow hexagonal prism shape. The isothermal crystallization and growth kinetics of cefluosil were further studied. The crystallization kinetics of cefluosil were found to be described by the Johnson-Mehl-Avrami-Kolmogoro (JMAK) equation (when χ < 1), and the growth of cefluosil in the non-equilibrium stage is controlled by the coarsening energy. In this research, the thermodynamic and kinetic data of REEs in CaO–SiO2–CaF2–Ce2O3 system are supplied, which providing the theoretical basis for sustainable utilization of REEs in REE-bearing slag.

The viscosity and crystallization behavior of slag from co-gasification of coal and extraction residue from direct coal liquefaction residue at high temperatures

Co-gasification of coal and extraction residue (ER) of direct coal liquefaction residue (DCLR) is an efficient route for DCLR utilization. The synthetic ash samples of different composition were designed to investigate the crystallization of slag and its effect on slag viscosity to optimize co-feedstock of coal and ER. FactSage, XRD, SEM and single hot thermocouple technique (SHTT) were used to investigate crystallization behavior of slags. The viscosity-temperature curves were measured by the high temperature rotating viscometer. The results indicated that the slag viscosity and crystallization behavior are dominated by chemical composition. With the ratio of acid/basic oxides (A/B) increasing, slag viscosity at high temperature increased dramatically due to higher polymerization degree. The polymerized structure of poor atomic mobility limits the growth of crystallization, so the initial crystallization temperature increases and crystallization rate decreases. Meanwhile, the change of SiO2/Al2O3 (Si/Al) showed the similar influence on slag viscosity and crystallization. Fe2+ has stronger depolymerization ability than Ca2+ on aluminosilicates structure. The decreasing CaO/Fe2O3 ratio leads to low viscosity and then the slag crystallization tendency is observed increasing. However, Fe2+ does not involve anorthite crystallization reaction, so the change of slag viscosity and crystallization depends on the Ca/Fe of liquid phase. To obtain the smooth slag tapping of coal and ER in the entrained flow gasifier, the chemical composition ranges as 2.10 < A/B < 2.69, 2.0 < Si/Al < 2.5 and 1.0 < Ca/Fe < 1.20 for coal blending with ER as feedstock is proposed. In the end, a TCV prediction model was established (TCV = 180.2 + 0.67*Tliq + 1.33*CaO*Al2O3*(SiO2)2/[(SiO2 + Al2O3)*(88.2–49.68*α)], α = CaO/(CaO + Fe2O3)).

Metal–alloy induced crystallization of amorphous silicon

A comprehensive investigation of metal–alloy induced crystallization (MAIC) of amorphous silicon (a-Si) is presented. The crystallization processes in three microstructurally principally different, representative types of metal(-alloy)/a-Si systems, Alx(Ge1−x)/a-Si, AgxAl1−x/a-Si, and AlxZn1−x/a-Si, have been monitored by in situ heating x-ray diffraction (XRD) from 25 °C up to 475 °C, until crystallization of a-Si was completed. The obtained experimental results have been systematically compared to predictions obtained by applications of thermodynamic models based on calculations of interface and crystallization energies for the determination of so-called critical thicknesses and initial crystallization temperatures. From the investigation of the MAIC processes in the metal–alloy/a-Si systems, it has been demonstrated that the crystallization temperature and the crystallization kinetics can be well tailored and optimized by controlling the composition and microstructure of the metal alloys. This research, on the one hand, exposes the fundamental, principal role of interface thermodynamics on the crystallization processes and, on the other hand, opens new possibilities for the growth of technologically important, pure, crystalline semiconductor thin films at very low temperatures, as compared to the crystallization temperature of isolated, bulk semiconductor materials.

Nonisothermal crystallization behaviors of ethylene–acrylic acid copolymer and ethylene–acrylic acid copolymer/chloroprene rubber thermoplastic vulcanizate

Nonisothermal crystallization kinetics of ethylene–acrylic acid copolymer (EAA) and thermoplastic vulcanizate (TPV) based on EAA/chloroprene rubber (CR) were extensively studied using differential scanning calorimetry. Several methods, including the Avrami, Ozawa, and Mo equations, were carried out to analyze the process of nonisothermal crystallization kinetics of EAA and EAA/CR TPV. The results showed that the Avrami analysis modified by Jeziorny and a method developed by Mo could describe the nonisothermal crystallizations of pure EAA and the EAA/CR TPV very well. However, the Ozawa analysis did not give an adequate description. The crystallization processes of pure EAA and the EAA/CR TPV were accelerated by increasing the cooling rates. Moreover, the initial crystallization temperature and the crystallization termination temperature of EAA/CR TPV were higher than those of pure EAA at the same cooling rate, thus showing the nucleating function of CR in the beginning. While the crystallization half time of EAA/CR TPV was apparently longer than that of pure EAA, meaning that the more CR could cause the steric effect and retard the crystallization process of the TPV during the late stages of crystallizing. Although the CR phase of EAA/CR TPV could provide more nucleation sites, the presence of more CR phase must impose a much more significant confinement effect on the crystal growth of EAA. It was believed that this confinement effect overweighed the nucleation effect, thereby slowing down the overall crystallization rate.

Fabrication of branching poly (butylene succinate)/cellulose nanocrystal foams with exceptional thermal insulation

Branching poly (butylene succinate) (BPBS) nanocomposite foams incorporated with cellulose nanocrystals (CNCs) were prepared by supercritical CO2. Surface modification of CNCs by acetylation was achieved through replacing hydrophilic hydroxyl groups with hydrophobic acetyl groups, which improved the dispersibility of CNCs significantly. The crystallite sizes of CNCs and acetylated CNCs were calculated by Scherrer's formula as 25 and 19 nm, respectively. The initial crystallization temperature of diverse poly (butylene succinate) (PBS) specimens, a crucial factor for regulating cell nucleation type, increased remarkably by 11.8 °C as well as their storage modulus increased by 2 orders of magnitudes, due to branching reaction and bio-filler addition. BPBS/CNCs foam possessed a high volume expansion ratio as 37.1 times and displayed an exceptional thermal conductivity as 0.021 W(m K)−1. This study provided a promising potential strategy to develop exceptional thermal-insulation polymer foams for composite structures, energy conservation and environment protection.

Morphology and crystallization kinetics of Rubber-modified Nylon 6 Prepared by Anionic In-situ Polymerization

Abstract In this work, we modified nylon 6 with liquid rubber by in-situ polymerization. The infrared analysis suggested that HDI urea diketone is successfully blocked by caprolactam after grafting on hydroxyl of HTPB, and the rubber-modified nylon copolymer is generated by the anionic polymerization. The impact section analysis indicated the rubber-modified nylon 6 resin exhibited an alpha crystal form.With an increase in the rubber content, nylon 6 was more likely to generate stable α crystal. Avrami equation was a good description of the non-isothermal crystallization kinetics of nylon-6 and rubber-modified nylon-6 resin. Moreover, it is found that the initial crystallization temperature of nylon-6 chain segment decreased due to the flexible rubber chain segment. n value of rubber-modified nylon-6 indicated that its growth was the coexistence of two-dimensional discoid and three-dimensional spherulite growth. Finally, the addition of the rubber accelerated the crystallization rate of nylon 6.